There’s a crass old joke about how you can never buy beer, just rent it. Who would think that the same joke applies to book buying in the digital age?

But that’s the case. Many people who were unwrapping iPads, Amazon Kindles or Barnes & Noble Nooks last week and loading them with bestsellers or classics won’t have any idea how limited their rights are as their books’ “owners.”

In fact, they won’t be owners at all. They’ll be licensees. Unlike the owners of a physical tome, they won’t have the unlimited right to lend an e-book, give it away, resell it or leave it to their heirs. If it’s bought for their iPad, they won’t be able to read it on their Kindle. (The reverse, however, is true, if you register your Kindle.) And if Amazon or the other sellers don’t like what they’ve done with it, they can take it back, without warning.

All these restrictions “raise obvious questions about what ‘ownership’ is,” observes Dan Gillmor, an expert on digital media at Arizona State University. “The companies that license stuff digitally have made it clear that you own nothing.”

Typically, e-book buyers have no idea about these complexities. How could they? The rules and limitations are embodied in “terms of service” documents that Amazon, Apple, B&N and other sellers shroud in legalese and bury deep in their websites. That tells you how little they want you to know.

The rules are based, in turn, on the 1998 Digital Millennium Copyright Act, with which Congress hoped to balance the rights of copyright holders and content users. “In the digital environment, that’s always been the trickiest balance to strike,” Annemarie Bridy, a specialist in intellectual property law at the University of Idaho, told me. In those terms, the DMCA looks like a failure.

Both camps have important rights to protect. Let’s start with copyright owners.

In the non-digital world, copyright ends with the first sale of each copyrighted object. Under the “first sale” doctrine, once you buy a book, that physical book is yours to lend, give away, or resell. Copyright is safeguarded by the limitations of physical transfer — once the book is given or loaned, the original buyer no longer has access to it. If a library owns five copies of a book, only five borrowers can read it at the same time. Theoretically a book can be photocopied, but only at great effort and with a perceptible loss of quality.

In digital-dom, however, technology allows infinite copies to be made, with no loss of quality. Absent the usual restrictions, one could give away an e-book and still have it to read. Unrestricted transferability becomes a genuine threat to the livelihood of authors, artists, filmmakers, musicians.

So some limitation is sensible. That’s usually done through digital rights management, or DRM, which encodes copy or usage limitations into the digital file.

The question is whether the balance has tipped too far in favor of the booksellers, at the consumers’ expense. The answer is yes.

Amazon keeps your purchased content for free “in the cloud” for downloading to your readers as needed. You pay once for an e-book and can use it on all the Kindles you own. I can’t find any written promise by Amazon that this storage will always be free. If it announces a few years from now that henceforth there will be a monthly fee to store books purchased, say, more than 10 years ago, what rights will you have to resist? None.

It should be a top priority for Congress to clear out the murk. Buyers of e-books must have the explicit right to reformat their purchases and save backup copies for their own use, permanently. The sale of an e-book must be irrevocable.

On the other side, it must remain strictly illegal to make multiple unauthorized copies of any copyrighted work for distribution. Lending by libraries, one digital copy at a time, should be facilitated — it tends to widen the audience for books.

Clarify these rules of e-book commerce, and the book market will reap the benefit. The power of electronic booksellers over publishers might be reduced, and consumers would know what they were buying — and would own what they bought.

Leave the rules as vague as they are, and the victims will be authors, consumers and publishers.

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